1. Field of the Invention
The invention relates to a piston structure for two-directional axial motion in a piston cylinder containing liquid, the piston structure has a first side facing a first chamber and a second side facing a second chamber, a piston-rod is attached to the first or the second side of the piston, and in a recess formed in an outer portion of the piston an O-ring made of a resilient material and having a given cross-sectional diameter is placed which seals the wall of the piston cylinder. The invention further relates to a liquid feeder valve for allowing liquid flow-through in a certain amount or for a period of time from a pressurized source of liquid.
2. Description of Related Art
In liquid systems, for example in water-pipe systems there is often need for enabling dosage of liquid in certain amounts or for a period of time. There are valves which can be used for this purpose, for example the so called “Shell-valves”, such as water-closet flush valves. This application comprises a membrane and a relatively long and narrow conduit pipe with a cross-section of about 50 μm, which restricts the pressure of water and, by forming an auxiliary current, it blocks the flow path of the liquid after filling up a given volume. With use, the liquid flows through the thin passage in the same direction every time, and due to this, solid contaminants accidentally present in the liquid may choke up the narrow passage. In such case the valve must be disassembled and these contaminants can be removed from the conduit pipe by means of a thin wire pin which is after all a wearisome operation of maintenance.
U.S. Pat. No. 4,057,074 describes a valve design which is provided with an active piston displaceable in two directions. According to this description the design is operable even in case of great pressure differences existing between the two sides, by means of a spring used in one of the spaces of liquid. However, this element may in itself be a cause of failure.